The fabrication of integrated circuits (IC) in the semiconductor industry typically employs plasma to create and assist surface chemistry within a plasma reactor necessary to remove material from and deposit material to a substrate. In general, plasma is formed within the plasma reactor under vacuum conditions by heating electrons to energies sufficient to sustain ionizing collisions with a supplied process gas. Moreover, the heated electrons can have energy sufficient to sustain dissociative collisions and, therefore, a specific set of gases under predetermined conditions (e.g., chamber pressure, gas flow rate, etc.) are chosen to produce a population of charged species and chemically reactive species suitable to the particular process being performed within the chamber (e.g., etching processes where materials are removed from the substrate or deposition processes where materials are added to the substrate).
In order to aid in the manufacture of integrated circuits with uniform characteristics, manufacturers strive to use the most uniform processes possible from run-to-run. Accordingly, manufacturers strive to monitor the processes in the plasma processing chamber and adjust processing parameters if the plasma conditions vary beyond process-specific “normal” ranges.
There is a need for a low cost way to monitor and tune uniformity. Manufacturers of equipment meeting that need have a competitive edge in the market. One highly desirable avenue is improvements in tool performance and process monitoring where the cost of such improvements is small. The company that can enhance tool performance and process monitoring without driving up the tool cost is in a position to increase profit margins. In cyclical industries such as the semiconductor capital equipment industry, increased profit margins, whether in good times or in bad times, can have a dramatic impact on market penetration, especially during downturns.
Many process monitoring tools exist which are individually provided access to within the chamber. However, such individual placement increases the number of access ports that are required to be made into the plasma processing chamber. Each such access port requires a corresponding seal to maintain the vacuum environment, and, therefore, it adds to the complexity of the mechanical and electrical design of the plasma processing chamber. Accordingly, it is disadvantageous to need to maintain a large number of access ports to support an increasing number of tools.
Moreover, a single plasma chamber may be used for plural processes. The tools required to monitor a first process may not be the same as the tools to monitor a second process. Thus, either the plasma chamber has to be designed to have enough access ports to support permanently mounting the tools for both the first and second processes, or the tools must be changed between processes. This disadvantageously either (1) increases the number of access ports in the chamber, or (2) requires that the seals be broken in order to change the tools between processes.